[Pw_forum] constraints: planar and torsion angles

[Stefano Baroni]

thanks - SB

On Jul 14, 2010, at 5:36 PM, Norbert Nemec wrote:

> Hi there,
> 
> in case someone is curious about the commits I just checked in. Apart from some cleanup and some better logging output, I changed the internal handling of angle constraints:
> 
> Planar and and torsion angles used to be handled internally by their cosine. This had caused a problem for angles of 0 or 180 degree, where the derivative of the constraint would become zero and the constraint could not be enforced correctly. Specifically, this caused problems for planar benzene molecules that I tried to constrain.
> 
> With my change, the constraints are now internally handled as angle, the torsion angle as signed angle. It works beautifully for my test case. I adjusted the metadynamics code, otherwise, no code seems to be affected.
> 
> For the user, there should be no difference except in the case that someone would have explicitly specified torsion angles with incorrect sign in the input file. I doubt that anyone would do that...
> 
> Greetings,
> Norbert
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---
Stefano Baroni - SISSA  &  DEMOCRITOS National Simulation Center - Trieste
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